1. Field of the Invention
The present invention relates to an ultrasonic imaging probe used to be inserted in a body cavity or a lumen, such as a blood vessel, a vas, or a digestive organ, and to display a tomogram of the body cavity or the lumen.
2. Description of the Related Art
To treat angiostenosis portions taken as causes of cardiac infarction and the like, there have been used methods of performing percutaneous procedure for affected portions by using catheters, for example, a method of expanding an angiostenosis portion with a dilatation catheter having a balloon at its distal end, a method of implanting a tiny mesh tube called xe2x80x9cstentxe2x80x9d in an angiostenosis portion, or a method of resecting an angiostenosis portion by rotating a grinder or a cutter using an instrument called xe2x80x9catherectomy devicexe2x80x9d. Of these methods, a suitable one has been selected in accordance with the state of an angiostenosis portion and the state of a patient.
The ultrasonic probe has been mainly used in such percutaneous treatment of an angiostenosis portion for the purpose of observing the state of the angiostenosis portion so as to assist the decision to select the most suitable treatment means, and also observing the state of the angiostenosis portion after treatment.
The ultrasonic probe includes a flexible imaging core (having an ultrasonic transducer unit for transmitting and receiving ultrasonic waves to and from an affected portion and a drive shaft for rotating the ultrasonic transducer unit), and a sheath for covering the imaging core.
The inspection using an ultrasonic probe generally involves previously advancing a guide wire to an angiostenosis portion as an affected portion, carrying an ultrasonic transducer unit positioned in the vicinity of the distal end of the ultrasonic probe along the guide wire, and operating the ultrasonic transducer unit, thereby obtaining a continuous ultrasonic tomogram across the affected portion.
The ultrasonic probe fails to acquire an image signal unless an ultrasonic wave propagating substance for propagating ultrasonic waves is present between the ultrasonic transducer and the wall of a blood vessel, and therefore, a priming work of replacing air in the sheath with a liquid such as physiological saline is performed before insertion of the ultrasonic probe in a patient.
If the priming work is insufficient and thereby micro-sized bubbles remain on the surface of the ultrasonic transducer, the bubbles strongly reflect ultrasonic waves, to shield or scatter the ultrasonic waves, thereby significantly disturbing an image. For this reason, it is required to discharge bubbles from the sheath as much as possible.
To cope with such a problem, there has been proposed a method of enlarging a gap between the flexible imaging core and the inner wall surface of a sheath as much as possible, to ensure a specific flow rate of a liquid at the time of injecting the liquid from the proximal end side of the sheath, thereby removing bubbles remaining on the ultrasonic transducer unit by water flow.
This method, however, has a problem that if the gap between the flexible imaging core and the inner wall surface of the sheath is enlarged, the outer diameter of the sheath becomes necessarily large, to degrade the ability of the sheath to pass through a small-diameter blood vessel affection portion or to reach such a small-diameter blood vessel affection portion. In this way, there exist two inconsistent requirements of enlarging the flow passage for priming and reducing the outer diameter of the probe.
Another problem of the conventional sheath is that since the sheath, if used for a blood vessel, is as long as a value in a range of about 120 mm to 180 mm, even when a priming liquid is injected at a high pressure on the proximal end side, the pressure cannot be transmitted to the vicinity of an ultrasonic transducer on the distal end side, thereby failing to perfectly remove bubbles remaining on the ultrasonic transducer.
An object of the present invention is to provide an ultrasonic probe capable of efficiently discharging bubbles remaining inside the probe with less water flow, and also capable of reducing the diameter of the probe while keeping a high quality of an ultrasonic tomogram.
To achieve the above object, according to an aspect of the present invention, there is provided an ultrasonic probe including a sheath having a distal end insertable in a body cavity or a lumen, a proximal end having an injection port allowing an ultrasonic wave propagating liquid to be injected through the injection port, and a passage extending from the proximal end to the distal end, a drive shaft, having a distal end and a proximal end, for transmitting a mechanical drive force from the proximal end to the distal end, the drive shaft being disposed in the passage of the sheath, and an ultrasonic transducer provided at the distal end of the drive shaft, wherein a gap between the inner surface of the passage and the outer periphery of the drive shaft on the distal end side of the sheath is smaller than that on the proximal end side of the sheath.
With this configuration, since the flow passage is formed such that the gap between the outer periphery of the drive shaft provided in the sheath and the inner surface of the sheath becomes narrower on the distal end side than on the proximal end side, the flow characteristics such as the flow velocity, flow rate, and the flow pressure of the ultrasonic wave propagating liquid flowing from the proximal end are rapidly improved at a portion where the gap becomes narrow, and the flow characteristics of the ultrasonic wave propagating liquid are also improved in the vicinity of the transducer unit. Accordingly, it is possible to remove bubbles remaining in the vicinity of the ultrasonic transducer by the flow of the ultrasonic wave propagating liquid, and hence to keep a high quality of an ultrasonic tomogram formed by the ultrasonic transducer.
The passage preferably has a change portion whose inner diameter is changed.
With this configuration, since the flow passage becomes narrower on the distal end side than on the proximal end side, the center axis of the sheath is more closely aligned with the drive axis of the drive shaft, with a result that the drive of the drive shaft provided in the sheath can be stabilized at the distal end. As a result, it is possible to form a stable ultrasonic tomogram by the ultrasonic transducer.
The outer diameter of the sheath at the distal end is preferably smaller than that at the proximal end.
With this configuration, since the outer diameter of the sheath is smaller on the distal end side than on the proximal end side, it is possible to easily insert the sheath in a body cavity or a lumen.
The ultrasonic probe preferably further includes a discharge port allowing air in the sheath and/or the ultrasonic wave propagating liquid to be discharged out of the discharge port.
With this configuration, since the discharge port for allowing air in the sheath and/or the ultrasonic wave propagating liquid to be discharged out of the discharge port is provided at the distal end of the sheath, it is possible to remove air remaining in the sheath, together with the ultrasonic wave propagating liquid, by the flow of the ultrasonic wave propagating liquid.